Investigation of the Compound Strength of Hybrid Casting Components with Different Variations of Coated and Undercut Sheet Metal

Abstract

Lightweight design can reduce CO2 emissions and improve energy efficiency, especially in the fuel-intensive transportation sector. Multi-material design approaches can combine specific properties of materials for effective lightweight design. A multi-material component made from two metals used widely in industry could combine the exceptionally lightweight properties of aluminum with the strength and structural integrity of steel. However, joining aluminum and steel is a challenge due to their different thermo-physical properties and the possible formation of brittle intermetallic phases. In hybrid casting, aluminum is cast around a steel sheet insert in a high-pressure die casting process to produce complex parts. In a first approach, a cold gas sprayed aluminum coating on the insert was tested as a bonding agent between the steel substrate and the molten aluminum. The joint was achieved by a combination of metallurgical bonding and micro-clamping. As a second option, surface structures with undercuts were applied to the steel sheet by modified cold rolling, which allowed the molten aluminum to flow into the channels and interlock with the solid steel. Different orientations of the structure on the insert were tested. In addition, the combination of both approaches was used to potentially enhance the positive effect of the pretreatment techniques. Given the critical importance of joint strength, the quality of these approaches was tested by static tensile tests and dynamic fatigue tests. The results show that the joint by coatings is strongly influenced by the process temperature. The improvement of the joint by the surface structure depends on its orientation to the melt flow.